LI QIAOYAN (2010-01-22). Assessment on the performance of the enhanced displacement ventilation system in the tropics. ScholarBank@NUS Repository.

Abstract:

Displacement Ventilation (DV) system is used to improve the thermal comfort and Indoor Air Quality (IAQ) in buildings in an energy-efficient manner. However, in an office environment served by DV system with low floor to ceiling height and heat load, the temperature stratification is found to be less significant as compared to large spaces with high floor to ceiling height and heat load. The thermal comfort of occupants in small spaces served by DV system is also less acceptable. In view of these limitations of the conventional DV system, an enhanced 4-fan DV system was developed and evaluated by Sun (2010). It is found that the 4-fan system has significantly improved the thermal microenvironment around occupants as compared to the conventional DV system. However, the draught risk and energy consumption issues have become a problem with the 4-fan system. Hence, a 2-fan enhanced DV system is developed in this study to overcome these problems.
Experiments were carried out in a mock-up office at the National University of Singapore. Both objective measurements and subjective assessments were conducted to investigate the vertical temperature profiles, thermal comfort, thermal acceptability and contaminant transportation by varying the supply air temperature of 22?0.5, 24?0.5 and 26?0.5?C. Objective measurements included air velocity, air temperature, relative humidity (RH), etc. Subjective assessment was performed by means of questionnaire using thirty-two tropically acclimatized students. A breathing thermal manikin was also used to simulate human subjects in this study.
Results of the 2-fan study are similar to the 4-fan system with an improved temperature distribution. The air flow around human body is significantly improved by the 2-fan system. The vertical temperature profiles became steeper between 0.6 m and 1.7 m height when the fans were applied. It demonstrates that the fans are effective in bringing the cooler air to the subjects.
Results of the thermal sensation and thermal comfort are quite different from the 4-fan system. The fans in the 2-fan system are placed in more appropriate locations to provide cooling and reduce draught around the human body as compared to the 4-fan system, especially at higher ambient temperature of 26?C. Hence, it is more effective for the 2-fan system to improve the microenvironment of the occupants.
The 2-fan system also helps to save more energy as it consumes less electricity than the 4-fan system. This promotes energy-efficiency by reducing the carbon emission.
However, the pollutant transportation study shows that, if there are polluting source in front of the occupant, the concentration of pollutant in the inhaled air is higher for the 2-fan enhanced system as compared to the conventional DV system. A more comprehensive study is needed for the pollutant study.